This application claims the priority of German Patent Application Ser. No. 100 41 329.3, filed Aug. 23, 2000, the subject matter of which is incorporated herein by reference.
The invention relates to a permanent magnet excited rotor for an electric drive having a rotor plate pack and permanent magnets.
Nowadays, machines or devices such as, for example, machine tools are expected, in the range of lower revolutions, to comprise a duty rating which increases in linear manner with the number of revolutions. There is expected of an AC motor, from the rated number of revolutions up to the maximal number of revolutions, a substantially constant duty rating.
AC type main drives are, as a general rule, configured as asynchronous devices which satisfy the first requirement mentioned above up to the rated number of revolutions. The second requirement can also be satisfied, from the rated number of revolutions, with the asynchronous technique in a simple manner, since the air gap flux can be affected, and weakened, in direct manner, by way of the output voltage of a converter.
However, within the range of main drives, the permanent magnet excited AC motor is gaining in importance, primarily due to the fact that such a motor has a higher power density and, associated therewith, it allows a more compact motor configuration.
Problems do arise in the utilization of main drives in the asynchronous technique by permanent magnet excited motors primarily in the realization of the range of constant duty behavior commencing from the level of the rated number of revolutions. To satisfy this requirement is much more difficult in the case of a permanent magnet excited motor and it requires a greater economical effort.
The effectiveness of the field weakening of permanently excited or permanent magnet excited main drives is largely a function of the design of the plate section of the rotor, whereby the following requirements are to be satisfied for the inductivities in the longitudinal axis (d) and the transverse axis (q):
xe2x80x83Lq as feasiblexe2x80x94small
Ld as feasiblexe2x80x94large
Lq less than Ldxe2x80x83xe2x80x83(1) 
It is an object of the present invention to provide a rotor plate section which satisfies the above-mentioned requirements with respect to technical considerations, and also with respect to considerations of economics.
In accordance with one of the aspects of the present invention this object is achieved by a permanent magnet excited rotor for an electric drive, comprising a rotor plate pack and with permanent magnets, in which the rotor plate section is provided, for the purpose of raising the magnetic transverse resistance for the transverse axis of the rotor, with pole gaps.
In case of greater axis heights, it has been found advantageous in the technical aspect to arrange the magnets at the air gap and not in the rotor plate section, whereby the permanent magnets are disposed on the outer surface of the rotor plate in such a way that these magnets are disposed, during the assembly of the rotor in a stator, at the air gap between the rotor and the stator. Due to this, inter alia, a larger active-part utilization is achieved.
For reasons of utilization and for the purpose of an enhanced upper field behavior, the pole gaps are preferably configured in such a way that a pole coverage of the outer surface of the rotor plate with permanent magnets is in the range of from about 70% to about 80%.
In accordance with a further advantageous embodiment of the invention, the distance of depth of the pole gaps in the rotor plate is greater than the distance of width of the air gap provided between the rotor, mounted in a stator, and the stator.
It is, furthermore, advantageous that the pole gaps are disposed in the rotor plate pack in equidistant manner.
With respect to the manufacturing process, it is advantageous that the pole gaps are directly disposed at the air gap, particularly when they are produced by milling into the upper surface of the rotor plate pack.
Alternatively, the pole gaps can be arranged in the rotor plate section in covered manner, particularly by being stamped or punched into the rotor plate pack.
Furthermore, the pole gaps can be filled with an amagnetic material. This can comprise fill bodies such as, for example, plastic-synthetic rods, or by pouring an amagnetic material into the pole gaps.
The concept of the invention provides the design of a permanent magnet excited electric drive with a stator with a three-phase stator winding with a predetermined pole pair and with a rotor in accordance with the invention, which drive satisfies the above-mentioned requirements of a main drive, whereby such a drive can be operated, by way of field weakening at varying number or rotations, in a range of constant efficiency or capacity or output.